Clostridium are characterized as spore-forming, anaerobic, Gram positive bacilli. The species, Clostridium perfringens, can be subdivided into subspecies. Five subspecies have been described. These subspecies are generally known as “type” A-E. All subspecies produce several toxins, both major and minor toxins. The four major toxins are the alpha, beta, epsilon and iota toxin. All C. perfringens types produce the alpha-toxin. The beta-toxin is produced by C. perfringens types B and C. In addition, a range of minor toxins is produced by all C. perfringens types.
One or more of these various toxins can play a role in C. perfringens related pathogenesis. Type A is known to be pathogenic for various birds, man, cows and pigs. Type B is mainly pathogenic for lamb, sheep and goat, and causes “lamb dysentery” and haemorrhagic enteritis. Type C is pathogenic for man, sheep, calf, lamb, pig, and bird. C. perfringens can cause “struck”, haemorrhagic enteritis, necrotic enteritis and enterotoxemia.
Necrotic enteritis (NE) is an economically important enteric disease of birds, for example poultry, caused by Clostridium perfringens. The disease is usually controlled by antimicrobial drugs administered at prophylactic doses either in water or feed. However, there is concern about the routine prophylactic use of antimicrobial drugs in food animal production because of their contribution to resistance problems. If antimicrobial drugs were banned for such purposes in North America, there might be an increase in NE in poultry, for example chicken flocks, as has happened in Scandinavia (12).
Although vaccination offers an alternative approach to antimicrobial drugs in control of the disease, very little is known about immunity to NE. However, there has been considerable work on immunity to C. perfringens in other circumstances, since it is a cause of gas gangrene in people. This has identified the alpha-toxin, a phospholipase C exoenzyme, both as a major virulence factor and as an important immunogen. For example, a genetically engineered vaccine inducing alpha-toxin (amino acids 247-370) serum antibodies was shown by Williamson and Titball (34) to neutralize hemolytic activity of the toxin and to provide protection against C. perfringens in mice. Bennett et al. (5) showed that a recombinant Vaccinia virus vector expressing the non-toxic C-domain region of the alpha-toxin protein provided antibody-mediated protection against experimental toxin challenge. More recently, Stevens et al. (30) showed significant prevention of gas gangrene in mice by immunization using the C-terminal domain of the alpha-toxin (amino acids 247-370). In addition, there is evidence based on naturally occurring antibodies or maternal vaccination that antibodies to alpha-toxin are involved in immunity to NE (10,19). However, the importance of alpha-toxin or any other protein in immunity to NE in birds, for example chickens, remains to be demonstrated, and one study has shown the immunizing effects of alpha-toxin minus mutants (32). A recent study also demonstrated that an alpha-toxin minus mutant produced NE experimentally in chickens, demonstrating that factors other than alpha-toxin are important in the pathogenesis of NE (14). Other studies have shown that the immunizing ability to protect against NE was associated with virulent rather than with avirulent C. perfringens (32).
While the prior art has demonstrated some immunizing effect of whole-cell C. perfringens in chickens, the basis of this immunity is poorly understood. NE is usually controlled by antimicrobial drugs but, if these are unavailable or not used, there is currently no other simple way to control infection. Therefore, there is a need for novel vaccine for controlling Clostridium perfringens in birds.
An object of an aspect of the present invention is to provide a novel vaccine for controlling Clostridium perfringens in birds.